A source close to the Celtics confirmed that Stevens' deal is for six years and $22 million. Yahoo! Sports earlier reported terms of the contract. The Celtics have scheduled an 11 a.m. ET news conference Friday to introduce Stevens.

Stevens' hire drew reactions from players and coaches throughout the league, including legendary former coach Phil Jackson, who tweeted his thoughts.

Congrats, Danny Ainge, on hiring Brad Stevens. He has the demeanor of a composed leader. Hope he's got the hide of a rhino for NBA grind.

The move turns the tradition-bound franchise over to a mentor who is younger than Garnett and wasn't yet born when Bill Russell won his 11th NBA championship in 1969 (or even when John Havlicek added two more in the 1970s). It's the first time the Celtics have hired a college coach since Rick Pitino in 1997, and their first coach with no NBA experience of any kind since Alvin "Doggie" Julian gave way to Red Auerbach in 1950.

"Though he is young, I see Brad as a great leader who leads with impeccable character and a strong work ethic" Celtics general manager Danny Ainge said in a release. "His teams always play hard and execute on both ends of the court. Brad is a coach who has already enjoyed lots of success, and I look forward to working with him towards Banner 18."

A source with direct knowledge of the situation told ESPN.com's Andy Katz that the Celtics targeted Stevens as soon as the Rivers deal with the Clippers was finalized. The Celtics contacted Stevens a week ago. The two sides had phone conversations, and the Celtics were waiting for Stevens to say yes. Ainge and the Celtics' ownership group flew to Indianapolis on Wednesday morning for their one and only in-person meeting with Stevens, and he accepted the job there.

According to the source, the Celtics believe Stevens can be their head coach for a "long time,'' and they love his basketball mind, character and ability to relate to players. The source said the Celtics wanted to go for a coach who was highly respected. The Celtics talked to a few other candidates, but Stevens was the first, and throughout the past few years, whenever talk among the staff turned to a Rivers successor, Stevens' name was on the list.

Stevens had spent the past six years coaching Butler, leading the Bulldogs to back-to-back national championship games in 2010 and '11. He has a career winning percentage of .772 and never won fewer than 22 games in a season.

Stevens takes over a team that is three seasons removed from an appearance in the NBA Finals; the Celtics won their unprecedented 17th championship in 2008. But with Garnett and Pierce showing signs of slowing down in this year's playoffs, when Boston was eliminated by the New York Knicks in the first round, Ainge has decided to rebuild.

He allowed Rivers to take over the Clippers, extracting a first-round draft choice in return. Amid last week's NBA draft, the Celtics and Nets agreed to a deal that would send Garnett and Pierce to Brooklyn in exchange for a package of players along with three first-round draft picks.

Now, Stevens will be the one to work with those young players.

"Our family is thrilled for the opportunity given to us by the leadership of the Boston Celtics, but it is emotional to leave a place that we have called home for the past 13 years," Stevens said in a release issued by the university. "We truly love Butler University and Indianapolis, and are very thankful to have had the opportunity to celebrate so many wonderful things together."

At age 36, Stevens will be the youngest active coach in the NBA, two years ahead of Orlando's Jacque Vaughn.

At Butler, Stevens was 166-49 -- the most wins for any Division I coach in the first six years of his career. In 2009-10, the Bulldogs went 33-5, including the Horizon League's first 18-0 conference record, a 25-game winning streak and an appearance in the NCAA title game, where they lost to Duke 61-59 when a last-second, half-court shot bounced off the backboard and rim and out.

"Brad has given his talent to our university with exceptional generosity, integrity, and humility," Butler president James M. Danko said, calling Stevens "a beloved member of our community."

Butler athletic director Barry Collier also praised Stevens for his time at Butler, posting a message on Twitter.

@BUADCollier: Many thanks to Coach Brad Stevens for his outstanding leadership at #Butler. A fantastic person and we wish him well.

"That shows you the faith we had in Brad and the commitment we made to him," Collier said in a news conference at the school on Wednesday night. "I didn't treat it as inevitable [that he would leave]. I looked at it like every year Brad was our coach, it was another good year for Butler."

"I think everyone is surprised. ... You think of Brad as one of the great college coaches," the Team USA coach told Katz. "He's an outstanding coach. He's at a time, he's young, I can see him, wanting to do something different. He's terrific. It's a great hire for the Celtics."

Krzyzewski, who himself has flirted with jumping to the NBA, thinks earning the respect of his new players won't be an issue with Stevens.

"He'll have respect. He's accomplished. Players respect success. He's had great success right away. So I don't think he'll have any problem with the players respecting him," Krzyzewski said. "They'll respect him. They respect excellence. He has it. It's a terrific hire. I'm a friend of his and I wish him the very best and I'll be pulling for him.

"To take over one of the most storied franchises in sports in an incredible opportunity, I can understand him doing it. In 1990, I almost did it with the Celtics. Dave Gavitt had just taken over. I can understand it."

While a new start lies ahead for Stevens and the Celtics, Butler is still left to fill the coach's enormous shoes.

"We have done everything we can to keep Brad here at Butler; however, the Celtics team has offered Brad and his family a unique opportunity with which no university can compete," Danko said.

Information from ESPN.com's Andy Katz and Jeff Goodman and The Associated Press was used in this report.